Eddy covariance measurement of carbon dioxide and methane fluxes from UK inland waters

It is now recognised that freshwater ecosystems are active components of the global carbon cycle, and that human activities have greatly modified natural aquatic biogeochemical processes. In some inland waters, this has led to large greenhouse gas (GHG) emissions to the atmosphere. However, these emissions are highly variable in time and space and are consequently hard to measure at scales required to inform GHG budgets. High-frequency, field-scale monitoring techniques such as eddy covariance offer the potential to capture these important but poorly understood emissions. A network of eddy covariance towers has been established across four UK inland waters, encompassing a Scottish loch, a Northern Irish lough, an English lake and a Welsh reservoir. High temporal resolution methane and carbon dioxide flux data from the respective water bodies have been generated from 2022 onwards.  Fluxes of carbon dioxide exhibited strong seasonality, with uptake occurring in the summer and release to the atmosphere in the winter. Seasonality was less clear for methane fluxes, though highest emissions to the atmosphere generally occurred in the spring and summer. Methane fluxes were positively correlated with chlorophyll-a at sites where supporting water quality data were available, with a statistically significant correlation evident at one site, indicating productivity as a key control on emissions. All sites were net sinks for carbon dioxide and net sources of methane over the monitoring period. This network of eddy covariance flux towers is generating new scientific understanding concerning the processes that drive aquatic fluxes of carbon dioxide and methane, and the contribution of inland waters to national GHG budgets.